Side scrolling multiple objects in Cocos2d - ios

Question

I'm having a problem with side scrolling in Cocos2d. What the situation is, is that i have a sprite that contains multiple other sprites know as actions. The user can swipe back and forth horizontally to scroll through the multiple actions. Whats happening now is that it is very jerky and seems to lag and not a smooth scroll but just very choppy. Not sure what the problem is, I've tried to change the time of the animation but that doesn't seem to work.
- (void)translateInventoryForSwipe:(int)xTranslationValue {
NSArray* tempArray = [NSArray arrayWithArray:self.slotsCenterCoordinates];
[self.slotsCenterCoordinates removeAllObjects];
for (NSNumber* i in tempArray) {
NSNumber* newXCoordinate = [NSNumber numberWithInt:[i intValue] + xTranslationValue];
[self.slotsCenterCoordinates addObject:newXCoordinate];
}
[self updatePositionOfActionsInInventory];
}
this method takes in the delta x of the two touches from the parent view. (current touch minus previous touch) This sets the centre coord of all the actions in the scrolling view.
- (void)updatePositionOfActionsInInventory {
for (int inventoryCounter = 0; inventoryCounter < self.inventorySize; inventoryCounter++) {
FFAction* action = [self.actions objectAtIndex:inventoryCounter];
if (action != self.actionBeingDragged)
[self placeAction:action atIndex:inventoryCounter];
}
self.tempAction = nil;
}
- (void)placeAction:(FFAction*)action atIndex:(int)index {
const float yCenterCoordinate = self.boundingBox.size.height/2;
NSNumber* xCenterCoordinate = [self.slotsCenterCoordinates objectAtIndex:index];
CGPoint centerPointForActionAtIndex = ccp([xCenterCoordinate floatValue], yCenterCoordinate);
CCAction* updatePositionAction = [CCMoveTo actionWithDuration:0.03f position:centerPointForActionAtIndex];
if ([action.view numberOfRunningActions] == 0 || self.tempAction == action) {
[action.view runAction:updatePositionAction];
[action.view released];
}
}
this part is from the parent sprite that handles the touch:
CGPoint currentTouch = [self convertTouchToNodeSpace:touch];
CGPoint previousTouch = [touch previousLocationInView:[touch view]];
int translationPoint = currentTouch.x - previousTouch.x;
[self.inventory translateInventoryForSwipe:translationPoint withPoint:currentTouch];
this then sets the action coordinate mimicking a scrolling effect. I'm not sure where its causing the jerky motion but if anyone has any help on the situation it would be awesome!

Answer 1

Assuming all of the complexity in your code is not required, there are several aspects to consider here, I'll go through them one by one.
First, memory allocation is expensive and a lot of it is done in every call of translateInventoryForSwipe:. A whole new NSArray is created and the self.slotsCenterCoordinates is repopulated. Instead, you should iterate the action sprites and reposition them one by one.
This brings us to the second aspect, which is the use of CCAction to move the sprites. A new CCAction is created for every sprite, again causing delay because of the memory allocation. The CCAction is created, even if it would not be used. Also, the use of actions might be the main cause of the lag as a new action won't be accepted until the previous has finished. A better way to do this would be to directly reposition the sprites by delta instead of assigning actions for repositioning. The action is not required to get smooth movement as the frequency of calls to translateInventoryForSwipe: will be high.
You should also consider using float to send the delta value to the method instead of int. The touch coordinates are floats and especially on retina devices this matters as the distance of two pixels is 0.5f.
Based on these aspects, here is a template of what a fixed method could look like. This is not tested, so there may be errors. Also, I assumed that action.view is the actual sprite, as the actions are assigned there.
- (void)translateInventoryForSwipe:(float)xTranslationValue {
for (FFAction *action in self.actions) {
if (action == self.actionBeingDragged)
continue;
// Position the items manually
float xCoordinate = action.view.position.x + xTranslationValue;
float yCoordinate = self.boundingBox.size.height/2;
action.view.position = ccp(xCoordinate, yCoordinate);
}
}